The present invention relates to a liquid delivery apparatus and a liquid delivery method. More particularly the present invention relates to a liquid delivery apparatus and a liquid delivery method for delivering a small volume of liquid while controlling the flow thereof in a micro fluid passage.
In recent years, various bio-sensors have been developed for use as medical checkup chips in POCT (point of care test) applications at clinics or homes. Many of these bio-sensors are card-type devices having a micro fluid passage structure called μTAS (micro total analysis system). In view of simplification of the device structure, bio-sensors of this type require technologies for quantitatively delivering and distributing small volumes of liquid without use of a mechanical valve.
For example, Thilo Brenner et al., “Flow switch based on Coriolis force”; 6th International Conference of Miniaturized Chemical and Biochemical Analysis Systems (μTAS2003), October 2003; pp. 903-906 discloses a structure that distributes a fluid selectively among two chambers by using a Coriolis force. The Coriolis force is an apparent force (a kind of inertial force) that acts on an object, which moves on a rotating coordinate system, in a direction opposite to the direction of rotation (perpendicular to the direction of motion) with a strength proportional to the rotation speed and the moving speed of the object. Referring to FIG. 14, a rotary platform 1 has a fluid passage 2 connected to a chamber on the supply side (not shown) and fluid passages 4A, 4B that branch from the fluid passage 2 and are respectively connected to post-branching chambers 3A, 3B. The fluid passages 2, 4A, and 4B constitute a branching structure of inverted Y-like shape. The liquid in the supply chamber is caused by centrifugal force to flow through the fluid passage 2 into either the fluid passage 4A or 4B. When the rotary platform 1 rotates clockwise in plan view as indicated by a symbol R1, the fluid receives a Coriolis force acting counterclockwise. This results in that the fluid flows into the fluid passage 4B positioned at the counterclockwise side with respect to the outlet of the fluid passage 2 as indicated by an arrow 5B. Contrarily to this, when the rotary platform 1 rotates counterclockwise in plan view as indicated by a symbol R2, the fluid receives a Coriolis force acting clockwise in plan view. This results in that the fluid flows into the fluid passage 4A positioned at the clockwise with respect to the outlet of the fluid passage 2 as indicated by arrow 5A.
Experiments and simulations described in the above-mentioned prior art document show that under the condition where the fluid passage is 360 μm in width and 125 μm in depth, if the rotation speed of the rotary platform 1 is not lower than about 3,300 rpm, then the fluid can be selectively delivered into either one of the fluid passages 4A and 4B depending on the rotation direction of the rotary platform 1. However, the rotation speed decreased to about 2,000 rpm or lower causes that the fluid flows into the other fluid passage that is not selected and the rotation speed decreased to about 1,000 rpm or lower causes that the amount of incoming fluid becomes equal between the fluid passages 4A and 4B. In other words, the branching structure having the inverted Y-like shape shown in FIG. 14 can not achieve the selective distribution of liquid under the condition where the rotation speed is relatively low.